Ignition circuit



w. o. KENNINGTON 1,976,260

IGNITION CIRCUIT Filed Feb. 16, 1934 INVENTOR ATTORNEY Patented Oct. 9, 1934 UNED STATES PATENT OFFICE IGNITION CIRCUIT Application February 16, 1934, Serial No. 711,473 In Great Britain January 25, 1933.

3 Claims.

This invention relates to electrical coil ignition circuits of internal combustion engines.

The main object of the invention is to provide efficient ignition at high engine speeds.

5 More specifically the object is to reduce the time required, after closure of the circuit breaker, for the current flowing through the primary winding of the ignition coil to acquire an ample value.

The present invention consists of a relay having a coil winding for connection in series with the main contact breaker, with the primary winding of the ignition coil and with a pair of its own contacts, a second coil winding and a resistance across said contacts, and a third polarizing winding, the relay being adapted to operate at a current Value which is between that which is injurious to the primary coil and the minimum requisite for ignition.

An embodiment of the invention is illustrated diagrammatically in the accompanying drawing.

In an ignition circuit, it is necessary for the current, when the main contact breaker breaks the circuit, to be of such a value that the spark in the secondary circuit is suflicient for ignition.

It is also necessary that this current be built up within the period between the make of the main contact breaker and the succeeding break. This period is inversely proportional to the speed of the engine. At high speeds, say from 4,000 R. P. M. upwards, therefore the period may become so short that the primary current cannot build up to the requisite value. The time taken by the current to build up from zero varies as a function of the applied voltage. Ignition can therefore be obtained at high speeds by using a relatively high voltage. With such a voltage, however, excessive current flows through the primary coil when the engine is running at low speeds. A resistance inserted in the circuit will cut down this current to a value which is not injurious to the ignition coil.

Referring now to the accompanying drawing, there is shown a battery a, and ignition coil with primary and secondary windings b and 0 respec- 'tively, and a main contact breaker cl with its associated condense-r e. In series with the primary winding 12 and the contact breaker d is a current coil f of the relay whose armature contacts g are also in the same series circuit. Across the contacts g is a holding coil h and a resistance 7' in series with one another. The contacts g are normally held closed by a spring k. In a parallel circuit, connected across the battery, is a third coil Z of the relay, this being a voltage or polarizing coil. The coil carries a constant current when the circuit is completed through the main ignition switch m.

The ampere turns of the coils h and Z should be approximately equal, although the latter coil is naturally a high resistance coil passing very little current, say something of the order of about 40 to 50 milliamperes, since it is always in circuit with the battery a when the ignition switch m is on. These three coils and the spring 7c are arranged so that when the circuit is closed through d, the contacts 9' are opened as soon as the current through the circuit a, b, g, (2 reaches a value which is injurious to the coil b. For example, when a battery of 12 volts is used with an ignition coil designed for a 6 volt circuit, the current should not exceed about 4 amperes. In such an arrangement the relay can be made to operate efiectively so that it will just open the contacts at a total value of about 300 ampere turns. Once the contacts g are open, coils Z and it keep them 7 open until the current falls below a value which is slightly less than the above mentioned operating value, whereupon the spring closes the contacts. This occurs of course when the main contact breaker d breaks the circuit, the relay operating in 30 step with the main contact breaker. The total resistance of coils f and h and resistance 7' should be such that for a current value existing when the contacts 9! are open, the voltage drop across the same is equal to the difference between the applied voltage and that for which the induction coil is designed.

It will thus be seen that the device automatically limits the primary current to a value which is below that which is injurious to the primary coil and above the minimum which produces a sparking voltage.

At low engine speeds the current has time to build up to at least the minimum for ignition, before the main contact breaker it breaks the 9 circuit. The relay however, prevents the current reaching an excessive value. At high engine speeds, the current, due to the excess applied voltage, still builds up quickly enough to a value sufficient for ignition purposes. Speeds as high 1 as 10,000 and even 12,000 R. P. M. are possible by the application of this invention. The limiting speed at which sparking fails is reached when the time between a make and break in the primary circuit is just less than the time required for the current to build up to the minimum value for ignition purposes. The pull-up time, or time lag of the relay is in excess of this build up time, so that at the highest speeds, say above 4,000

R. P. M. it does not operate: the contacts remary coil.

The voltage or polarizing coil Z allows less ampere turns to be used on coil 1 and this reduces the impedance of the circuit. It also pro duces some initial magnetism in the laminated core of the relay and thus reduces the work and time required for the current in coil j to open the contacts 9. An alternative to this coil Z is to give the laminated core of the relay a certain degree of residual magnetism.

Should the voltage of battery a fall below a certain value such as 6 volts, for example during the operation of a starting motor, the system operates as a normal ignition system, for the contacts 9 remain closed.

To obtain a quick break, the movable contact of the pair y can be resiliently mounted on the relay armature the arrangement being such that when the latter has acquired its fullmomentum, a lug on it pulls down the contact arm to open the circuit.

It is to be understood that no limitation of the scope of the invention is to be implied from or effected by the figures and values given above since these may be varied to suit any particular practical requirements that may have to be fulfilled.

What I claim is:

l. A current limiting device for coil ignition systems of internal combustion engines comprising a relay having a coil winding for connection in series with the main contact breaker, with the primary winding of the ignition coil and with a pair of its own contacts, a second coil winding and a resistance across said contacts, and a third polarizing winding, the relay being adapted to operate at a current value which is between that which is injurious to the primary coil and the minimum requisite for ignition.

2. An ignition system for an internal combustion engine comprising in series an ignition coil, a battery which is of higher voltage than that for which the coil is designed, a main contact breaker, and one coil and the armature contacts of a relay, said contacts being shunted by a second relay coil and a resistance whose combined ohmic resistance when in circuit cuts down the voltage across the ignition coil to its designed value, a third coil of said relay being connected across'said battery, said relay being designed to open its contacts at a current value therethrough slightly above that requisite for ignition.

3. A current limiting device for coil ignition systems of internal combustion engines comprising a relay having a coil winding for connection in series with the main contact breaker, with the primary winding of the ignition coil and with a pair of its own contacts, a second coil winding and a resistance across said contacts, the initial magnetism of the core of the relay being such that the current through said first coil winding operates said relay when it reaches a value which is injurious to the primary coil, so that said second coil winding and resistance are inserted in the primary circuit.

'WILLIAM OSCAR KENNINGTON. 

